Pipe heater



April 13, 1937. G. w. WATTS 2,076,871

PIPE HEATER Filed June 11, 1934 4 Sheets-Sheet l Freah Feed INVENTOR George MK Watts TTORNEY April 13, 1937.

4 Sheets-Sheet 2 Filed June 11, 1934 O O O O Feed 64 ,15

a w w a? 0 4 g Z Ll g 6 U/ M A 2 INVENTOR I George N Watts BY ATTORNEY G. W. WATTS April 13, 1937.

PIPE HEATER Filed June 11, 1934 4 Sheets-Sheet 5 INVENTOR George W Watts l/9M Ma/LA ATTORNEY April 13, 1937. G. w. WATTS 2,076,871

PIPE HEATER Filed June 11, 1954 4 Sheeis-Sheet 4 INVENTOR George W Waits ZMMA ATTORN EY agenda 13, 1937 2,076,871 PIPE HEATER.

George W. Watts, Whiting, Ind., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application we 11, 1934, Serial No. 729,986

10 Claims.

An object of my invention is to provide an i improved pipe heater in which is attained automatic and independent regulation of the temperatures of the oil being heated. A further obiect is the attainment of regulation of the heat input into the convection tubes. A still further object is the provision of an improved pipe heater or tube still useful in combination atmospheric and vacuum distillation units. A further object is the provision of means whereby the heat input in the convection section of a pipe heater is controlled in response to the temperature of the oil being heated in one or more banks of convection tubes. Other objects will appear as this description proceeds.

In the drawings which form part of the speciflcation Figure 1 is a sectional view of a, heater and fractionating columns constructed in accordance with my invention;

Figure 2 is a view similar to Figure l of an other form of the heater;

Figure 3 is a sectional view' along the line III-III of Figure 1; I

Figure 4 is a detailed view of a bridge wall and modification of the control dampers which form part of my invention;

Figure 5 is a detailed view similar'to Figure 4 of a modified type of damper;

Figures 6 and 7 are detailed views of additional modifications-of the damper; and

Figures 8, 9 and 10 are modifications of the 'arr'angement shown in Figure 1.

In Figure 1, I have illustrated a conventional type of heater or pipe still with a housing 2, a combustion chamber 3, and a convection section 4. The combustion chamber and convection sections are separated by a bridge or rear wall 5 which extends between opposite side walls of the housing and from the floor to a point adjacent the roof 6 of the housing. A flue I connected with V a stack (not shown) communicates with the con- 5 vection section I at the lower endthereof.

Fuel is'introduced for the purpose of combustion into the combustion chamber through nozzles or burners 8 which are preferably mounted on the lower part of the forward wall of the housing 50 but which may have any other suitable location. The hot products of combustion introduced into or generated in the combustion chamber 3 tend to flow upwardly in the combustion chamber, thence over the bridge wall 5, and thence down- 55 wardly through the convection section 4. The

tubes in the convection section are preferably disposed in a plurality of superimposed banks (shown in Figure 1 as banks 9 and Ill). The bridge wall is pierced with one or more ports 40 which are located at an intermediate part of the bridge wall. One bank of convection tubes In is disposed above the level of the ports 40 and another bank of convection tubes 9 is disposed below the level of the ports 40.

In the modification shown in Figure 1, rela- 1o tively cool oil is introduced into the lower bank of convection tubes 9, is partially heated therein and thence discharged through the line l0 into a fractionating column l2 wherein the vaporized oil is carried off overhead and the unvaporized 15 oil together with any condensate is discharged from the bottom of the column through line l3, and thence introduced for further heating in the pipe heater. I prefer the arrangement shown in Figure l, in which the unvaporized oil and condensate in line I3 is introduced into tubes disposed in the combustion chamber. In Figure 1 the oil is passed through rear wall tubes l4, thence front or bridge wall tubes Ila, thence roof tubes Mb, thence rear wall tubes I40, and finally into the upper bank of convection tubes I II, from which the heated oil is discharged through line l5 into the second fractionating column, IS. The precise arrangement of tubes in the combustion chamber may be modified to 30 suit the desires of the designer. Thus, for example, fioor tubes may be provided in the combustion chamber and the routing of oil through the floor tubes, walltubes' and roof tubes may be varied at will.

The discharge line H may be provided with a thermostatic control element or sylphon 22 which serves to regulate the fuel supplied for combustion through the control valve l9. This thermostat 22 is preferably located on the discharge end of the lower or preheating convection bank 9.

The ports 40 are provided with dampers or control elements II. In Figure 1 these are shown as being disposed for horizontal movement. The dampers l'l are placed in recesses 2|. These dampers or port closures are connected to a control unit 20 which may be of the solenoid type or any equivalent type and which in turn is directly connected to a thermostatic control 18 placed preferably on the line l5 at the discharge end of the upper bank of convection tubes I0.

In Figure 1, I have shown two fractionating towers, l2 and I6, which preferably may be atmospheric and vacuum columns respectively.

In the. modification illustrated in Figure 2 (in which the elements bear the same reference numerals as the corresponding elements in Figure l) the arrangement of the housing combustion chamber and convection section is generally similar to that of Figure l. I have shown, however, three banks of tubes in the. convection section and have shown a slightly diiferent arrangement oftubes in the combustion chamber. As stated before, however, the arrangement of tubes in the combustion chamber may be varied at the will of the designer. The bridge wall I have shown pierced by two sets of superimposed ports, an upper series of ports II and a lower series of ports a, each series of ports being provided with closures l1 and Ila. respectively arranged generally similarly to the closures described in Figure 1.

In this modification the relatively cool fresh feed is introduced into the lowermost bank of convection tubes 23, is passed therethrough and thence discharged through line 24 which conveys the preheated oil into the bridge wall tubes 25, thence through the front wall tubes a, and

thence through the upper bank of roof tubes 25b. The oil discharged from the roof tubes is conveyed through line 26 into the bank of convection tubes 9, from which it is discharged through line H into a fractionating column (not shown). The unvaporized oil plus condensate from this fractionating column, which is preferably maintained under atmospheric pressure, is discharged from the bottom of the column through a line It, then introduced into the combustion chamber wherein it is heated in bridge wall tubes l4, front wall tubes Ila, and then through roof tubes Mb, from which it is conveyed through line "a, to the upper bank of convection tubes Hi. The heated oil discharged from the upper bank of convection tubes II is 40 conveyed through line I! t6 a second fractionating column (not shown) which is preferably maintained under vacuum.

The lowermost bank of convection tubes 21 is preferably disposed below the level of the lower- 5 most ports "a. The intermediate bank of convection tubes 8 is preferably disposed below the level of the uppermost ports I and the upper bank of convection tubes III is disposed above the level of the upper ports 40.

The discharge line 24 is provided with a control element 22, preferably thermostatic or of the sylphon type, which acts through control valve l9 to regulate the amount of fuel introduced into the combustion chamber through the nozzles 8. The ports 40 are provided with closures or dampers l1 disposed in recesses 2i similarly to the ports in Figure l, and these closures or dampers are controlled through controls 20 and 20a which are responsive to the tempera- 60 ture of the 011, preferably the temperature at the discharge end of the convection bank It. The thermostat l8 disposed on the discharge line is, or equivalent element operates to control the control unit 20. The lower bank of ports 40a is similarly equipped with closures i'la which are in turn controlled through a control element 20a which is responsive to the temperature of the oil being discharged from the convection bank 8 as that oil affects the thermostatic or equivalent element Ida.

In Figure 4, I have disclosed a detailed drawing in section of a modified type of damper or port closure. In this modification the closures 75 21 are disposed on the convection side of the bridge wall and are arranged for horirontal movement, being supported by brackets 2|.

In the modification shown in Figure 5 the closures are of a sli gl tly diiferent type, being elements 2| which are disposed in recesses 30 built into the bridge wall and in which the closures or dampers move upwardly or downwardlyto vary the effective area of the port.

lnl'igureethedamperorclosurellisof the usual butterfly type arranged to revolve about a fixed axis in order to vary the effective area of the port.

In Figure 7, I-have shown the closure or damper as a plate 82 hinged on the support 83 which is located on the convection side of the bridge wa I In Figure 8, I have shown the modification of aheatersimilartotheheaterdisclosedinFigurel. Inthismodificationtheuppercoilof tubes in the convection section (the coil being designated "13") is'smaller than the bank of convection tubes disclosed in the lower part of the convection section and designated "A". The convection tubes A may be connected in any suitable manner with any arrangement of tubes in the radiant section of the furnace.

In Figure 9, I have shown a modification generally similar to Figures 1 and 8.- In this modification the convection bank of tubes B is relatively large and the convection bank of tubes A is relativedly small. In each of the modifications shown in Figures 8 and 9 the temperature of the oil discharged from the upper bank B operates to control the damper or closure l1 and the oil discharged from the lower bank of convection tubes A operates to control the fuel introduced through the nozzle 0.

In Figure 10, I have shown a modification in which both convection sections B and A are relatively large. In this modification I have shown B as the lower bank of convection tubes, the temperature of the oil discharged from which controls the damper or closure II, The oil discharged from the upper bank of convection tubes A operates to control the fuel introduced through the nozzle 8.

In each of the modifications above the damper or closure element is connected to and actuated by a control which is responsive to the temperature of the 011 being heated and preferably the temperature of the oil in a bank of convection tubes disposed above the level of the ports.

The operation of the apparatus which I have described above with reference to Figure l is as follows: The fresh feed is introduced into the convection coil 9 where it is preheated and then discharged into the atmospheric tower i2 which may be any conventional type of fractionating column such as bubble tower, flash drum, packed or baiile tower. The vaporized portion of the preheated oil is separated from the unvaporired portion. The condensate together with any unvaporized oil is discharged through line II from the bottom of the tower i2 and then is passed to the tubes in the combustion ghamber of the still and thence into the convection bank It. The heated oil is led into the vacuum tower it, which may be similar to the tower i2 or may be of any desired conventional type.

The preheated oil discharged from the convection bank 9 serves to regulate the amount of fuel introduced into the combustion chamber. This regulation is maintained by means of a thermostatic or sylphon control 22, which is reaovasn sponsive to the temperature of the preheated oil discharged from the convection bank 8 and which operates upon the control valve l9. If the temperature of the oil discharged from the convection bank 9 rises above a desired point,

the thermostat 22 and control valve l9 tend to diminish the amount of fuel introduced into the combustion chamber. Conversely, if the temperature of the oil discharged from bank 9 drops below a desired point, the control valve I9 is automatically opened to admit fuel into the combustion chamber.

In the conventional bridge wall furnace hot gases or products of combustion which are introduced into the combustion zone tend to flow upwardly in the combustion zone and thence over the top of the bridge wall and downwardly through the convection zone from which the hot gases are discharged into a stack. In this conventional type of bridge wall furnace the convection tubes at the uppermost part of the convection zone tend to become more severely punished with resultant deterioration of the tubes themselves and coking of the oil within the tubes-that is,-of course, relative to the convection tubes in the lower part of the convection zone. This punishment of the upper convection tubes is due to several factors such as radiant heat which is re-radiated from the roof of the furnace. It is also due to the fact that immediately after being discharged from the combustion zone the hot gases are relatively hotter' than they are after have been cooled by contact with a plurality of tubes in the convection zone. In the conventional bridge wall furnace it is sometimes difflcult to get a balanced heating of the convection tubes for this reason.

To operate my heater in the most flexible fashion I have provided means for varying the 40 amount of hot products of combustion so bypassed into the convection zone. These means comprise closures or dampers adapted to vary the eiiective area of the ports and at the same time to control the amount of gases permitted to 45 flow through the ports. In order to get satisfactory regulation of the amount of gases so by-passed I control the dampers or closures through a control element 20 which may be a solenoid or any equivalent structure which in 0 turn is responsive to the temperature of the oil being discharged from the upper bank of convection tubes Ill. Thus, as the oil being heated in the upper bank of convection tubes I0 tends to be overheated or too hot, the temperature 55 of the thermostat l8 rises. The thermostat acts upon the control 20 to open the damper or closure l1, permitting more hot gases to flow through the port and coincidentally diminishing the amount of gases which flows over the bridge wall 60 and down through the convection tubes III. This will tend to decrease the temperature of the oil being heated in the convection tubes I0. Conversely, when the temperature of the oil being heated in convection tube Ill sinks below a de- 65 sired point the temperature of the oil acts upon the thermostat 18 which in turn operates upon the control 20 to close the ports and lessen the effective area thereof. This results in diminishing the amount of gas which is by-passed through 70 the ports and coincidentally increasing the amount of gas which must flow upwardly over the bridge wall and down through the convection tubes ID. The amount of heat imparted to the convection tubes In and to the oil being heated 75 therein is thus controlled within desired limits.

Furthermore, in the case where the ports ll are relatively wide open, permitting a very appreciable quantity of hot gases to flow through the convection bank 9, there is at times a tendency to overheat the tubes in this convection bank 9. Where this overheating is experienced the thermostat 22 acting upon the control valve l9 operates to diminish the total quantity of fuel and the total quantity of hot products of combustion introduced into the combustion chamber. Thus the operation of the heater in toto is efiectively regulated within desired hunts.

In the modification shown in Figure 2 the operation of the heater is substantially the same in principle. In this modification I have shown three banks of convection tubes and two series of ports. The lowermost bank of convection tubes is a preheater bank 23 which corresponds to the bank 9 in Figure 1. The temperature of the oil discharged from this preheater bank serves to control and regulate the amount of fuel introduced into the combustion chamber. The effective area of the ports is controlled by means of dampers or closures which are responsive to the temperature of the oil being discharged from the convection bank In, while the eifective area of the ports 40a is controlled by dampers or closures which are in turn controlled by the temperature of the oil discharged from the con- I vection bank 9.

In this modification when the 011 in tubes Ill becomes overheated the thermostat IB operates to open the damper I1 and enlarge the effective area of the ports 40. Similarly, where the temperature of the oil being heated in the bank 9 tends to rise to too great a degree, the thermostat l8a operating on the damper l'la tends to enlarge the efiective area of the ports 40a,-

ineither case permitting hot gases to by-pass the bank of tubes immediately above the ports. It is obvious that where the temperature of the oil discharged from lines l5 and II drops below a desired point, the dampers are automatically closed, thus eliminating the by-pass (in part at least) and permitting more hot gases to contact the bank of tubes immediately above the ports.

If the B coil is relatively small, as compared with the A coil in the convection bank, as shown in Figure 8, the preferred arrangement will be to place the B coil in the upper part of the convection section. The A coil may well consist of two sections; one located below the B coil in the convection section and the other in the radiant section, or the coil may be divided as shown in Figure 2. The B coil controls the setting of the damper and the A coil controls the firing valves. TheB coil would be of such a size that the outlet temperature from B would be too high when all of the hot gases were passed through B and the firing was at the same time controlled to give the proper A temperature. The efiect of the damper control as controlled by B would be to pinch down on the amount of gas passed through B until the proper B temperature was secured. At the same time the A control would regulate the fire to keep the desired A outlet temperature. Obviously the unit would not function so well if the B coil were placed at the bottom of the convection section, for then it would be necessary to pass all of the hot gases through this coil. In this event the control would be secured through a regulation of the temperature of the gas and this would not be as effective as a regulation of the volume of the gas. With this arrangement the B coil would have to be made so that there would be insufficient heat pickup by it when all I of the. gas was sent through the convective part of the .A coil. Then some'gas wouldbe bypassed around the A coil to increase the average tem- 5 perature of the gas passing through the B coil. This, in turn, would drop the A temperature and would require more firing. For these reasons it is preferable to place the smaller B coil in the upper part of the convection section. It may also be observed that if both the A and B convection coils are small it is much better to place the B coil at the top of the convection section, forif it were placed at the bottom little control could be obtained through varying the amount of gas which goes through the A coil since a small A coil would not remove much heat. In the modification illustrated in Figure 9 the B coil is relatively large and the A coil is relatively small. If the B coil were placed at the bottom bypassing of gas around A would have little effect on either A or B, therefore the control would not be sensitive. However, if the B coil were placed at the top of the convection section the bypassing of gas around it would be very.

- effective in controlling the B outlet temperature, but would not have much eflect on the A outlet temperature. Consequently, with the B coil controlling the temperature and the A coil controlling the firing, the regulation is very sensitive and quite flexible.

If, as illustrated in Figure 10, both convection coils are relatively large, either may be placed at the, top or bottom of the convection section and good regulation will be secured in either case.

If, for example, the A coil is placed on top and the B coil below sensitive regulation is obtained if the E coil controls the gas by-pass and the A coil controls the firing. Witlr this arrangement, if the gas which is left to pass through A is not in sufiicient quantity or at the proper temperature to give the desired A outlet temperature, then the fuel will be increased-and this will result in an increase in the amount and temperature of the gas bypassed directly through the B coils. As a result, the damper will partially close to get the required B condition and the A coil will-receive more gas at a higher temperature. Through the interaction of the temperature and fuel control the proper conditions of heating A 5 and B may be readily obtained. On the other hand, if the B coil is placed on top the amount of gas passed through B will be regulated to give the proper temperature to B. If this results in too low a temperature for A the fuel will be in- 55 creased to get the A requirements and since this in turn will tend to increase the B temperature the damper will open and bypass gas around B. Again the regulation will be satisfactory for both coils.

60 In the modifications shown in Figures 1, 2, 8, 9, and- 10, I have disclosed the oil flowing from the top to the bottom of each of the coils in the convection section, that is, in a direction concurrent with the flow of the gases through the convec- 65 tion section. This would be advantageous where -75 maintained without upsetting the balance of the furnace. It will be apparent that efliclent operation of my furnace is obtained regardless of whether the convection tubes II are larger or smaller or the same size as the convection tubes 9 disposed below them. This is an advantage which is not found in the ordinary type of bridge wall heater, and I' contemplate as part of my invention the use of banks of convection tubes composed of tubes which may be larger or smaller than the tubes in the other banks in the convection zone.

My furnace is particularly suited to the heating of two or more oil streams undergoing cracking. For example, I may heat a gas oilstream to a temperature of 900 to 975 F. in one coil and a heavy naphtha stream in another coil to a temperature of 985 to 1100'1". for reforming. Still other streams, such as heavy residuum, cycle gas oil, virgin gas oil, etc., may be heated to other temperatures.

It will be understood that whereas the foregoing is a full and complete description of my invention, I am not limited therein except as expressed in the claims as follows.

I claim:

1. In a heater for fluids, a combustion chamber, a convection chamber, a bridge wall having ports therein interposed between said chambers, means for introducing hot products of combustion into said combustion chamber, means for causing the hot products of combustion to tend to flow upwardly in said combustion chamber, thence over said bridge wall and through the ports therein and thence downwardly through said convection chamber, fluid-confining tubes' in said combustion chamber and adapted to be heated by said hot products of combustion, an upper bank of fluid-confining tubes disposed above said ports and in said convection chamber, a lower bank of fluid-confining tubes disposed below said ports and in said convection chamber, controlled dampers for varying the area of said ports and at the same time varying the amount of hot products of combustion passed over said bridge wall and thence in contact with said upper bank of tubes, thermostatic means responsive to the temperature of the fluid at the discharge end of said lower bank of tubes for controlling said dampers and said port areas. and means responsive to the temperature of the fluid at the discharge end ofsaid upper bank of tubes for conv trolling the means for introducing hot products of combustion into said combustion chamber.

2. In a heater for fluids, a combustion chamber, a convection chamber, abridge wall interposed between said chambers, means for introducing hot products of combustion into said combustion chamber, fluid-confining tubes in said combustion chamber disposed to receive heat from substantially all of the products of combustion, banks of fluid-confining tubes in said convection chamber for conducting separate streams of fluid therethrough, means for connecting at least a part of the tubes in said combustion chamber to one of the banks of tubes in the convection chamber, a damper arrangement disposed within said bridge wall for by-passing a portion of the hot products of combustion around one of the banks of tubes in the convection chamber, means connected to the discharge end of one of the banks of tubes in the convection chamber responsive to the temperature of the stream of fluid passing therethrough for controlling the damper arrangement and regulating the quantity of hot products of combustion by-passed around one of the banks of tubes in the convection chamber and other means connected to the discharge end of another or the banks of tubes in the convection chamber responsive to the temperature of another separate stream of fluid passing therethrough for simultaneously controlling the means for introducing the hot products of combustion into said combustion zone.

3. In a heater for fluids, a combustion chamber, a convection chamber, a bridge wall interposed between said chambers; means for introducing hot products ot'combustion into said combustion chamber, fluid-confining tubes in said combustion chamber disposed to receive heat from substantially all of the products of combustion, banks of fluid-confining tubes in said convection chamber for conducting separate streams of fluid therethrough, means for connecting at least a part of the tubes in said combustion chamber to one of the banks of tubes in the convection chamber, a damper arrangement disposed within said bridge wall at a point lower than at least one of the banks of tubes in the convection chamber for passing a portion of the hot products of combustion therethrough without substantially contacting the bank of tubes in the convection section above said damper arrangement, means connected to the discharge end of the bank of tubes above said damper arrangement in the convection section responsive to the temperature of the stream of fluid passing therethrough for controlling the damper arrangement and regulating the quantity of hot products of combustion passed therethrough and other means connected to the discharge end of another of the banks of tubes in the convection chamber below said damper arrangement responsive to the temperature 01' another stream of fluid passing therethrough for simultaneously controlling the means for introducing the hot products of combustion into said combustion chamber.

4. The method of heating petroleum oil in an apparatus having a combustion chamber and a convection chamber which comprises flowing combustion gases through said combustion chamber, heating one stream of oil passing through said combustion chamber by substantially all of said combustion gases, conducting said stream of oil through a part of said convection chamber heated by only a part of the combustion gases, conducting another part of the combustion gases to another part of the convection chamber, regulating the quantity of combustion gases heating the aforementioned stream in response to the outlet temperature thereof, passing another stream of oil through the convection heating .chamber, heating it by all of the combustion gases and regulating the quantity of combustion gases flowing through said combustion chamber in response to the temperature of the last mentioned stream of oil leaving the convection chamber.

5. The method of heating petroleum oil in an apparatus having a combustion chamber and a convection chamber which comprises flowing combustion gases through said combustion chamber, heating one stream of oil passing through said combustion chamber by substantially all of said combustion gases, conducting said stream of oil through the upper part of said convection chamber, heating said stream of oil by only a part of the combustion gases, conducting another part .0! the combustion gases to a part of said convection chamber below the aforementioned 75 stream, regulating the quantity of combustion gases heating the aforementioned stream in response to the outlet temperature thereof, passing another stream of oil through the lower part oi said convection hamber and heating it by all 01. the combustion gases and regulating the quantity of combustion gases flowing through said combustion chamber in response to the temperature of the last mentioned stream of oil leaving the convection chamber.

6. In a heater for'fluids, a combustion chamber, a convection chamber, a bridge wall having ports therein interposed between said chambers, means for introducing hot products of combustion into said combustion chamber, means for causing part of the hot products of combustion to flow over said bridge wall and another part through the ports therein and thence downwardly through said convection chamber, fluid-confining tubes in said combustion chamber and adapted to be heated by substantially all oi said hot products of combustion, an upper bank of fluid-confining tubes disposed above said ports and in said convection chamber, a lower bank of fluid-confining tubes disposed below said ports and in said convection chamber, controlled dampers for varying the area of said ports to vary the amount of hot products of combustion passed therethrough and at the same time varying the amount of hot products of combustion passed over said bridge wall and thence in contact with said upper bank of tubes, thermostatic means responsive to the temperature of the fluid at the discharge end of said upper bank of tubes for controlling said dampers and said port areas, and means responsive to the temperature of the fluid at the discharge end of said lower bank of tubes for controlling the means for introducing hot products of combustion into said combustion chamber.

7. In a heater of the bridgewall type for heating petroleum oils, a combustion chamber, means for introducing hotproducts oi combustion into said combustion chamber, oil-confining tubes in said combustion chamber, a convection chamber, superimposed banks of oil-confining tubes in said convection chamber and adapted to be heated by hot products of combustion discharged from said combustion chamber, a bridge wall having ports therein interposed between said combustion and said convection chambers, said ports providing 'meanswhereby at least part of the hot products of combustion are introduced into said convection chamber without passing over the bridge wall and whereby convection tubes located above said ports are by-passed by said h'ot products of combustion, means for controlling the eflective area of said ports, to vary the amount of hot products of combustion passed therethrough, said means being responsive to the temperature of the oil at the discharge end of the bank of convection tubes located above said ports, and means responsive to the temperature of the oil in the convection tubes located below said ports for controlling the amount of hot products of combustion introduced into said combustion chamber.

8. A system for distilling petroleum oil comprising a heater of the bridge wall type, a first fractionating column, a second fractionating column, a combustion chamber in said heater, 2. convection chamber in said heater, a bridge wall having ports therein disposed between said combustion and said convection chambers, means for introducing hot products of combustion into said combustion chamber, means for conveying said hot products of combustion over said bridge wall and thence downwardly through said convection chamber, oil confining tubes in said combustion chamber. an upper bank 01' tubes in said convection chamber and disposed above the level oi said ports, a lower bank of tubes in said convection chamber and disposed below the level of said ports, means for causing oil to flow through said lower bank of tubes, thence to said first i'ractionating column wherein the vaporized oil is fractionated from the unvaporized condensate, means for conveying said condensate asa separate stream to said combustion chamber for heating therein, means for conveying the heated oil from said combustion chamber to said upper bank of tubes in said convection chamber for heating therein, means for conveying to said second iractionating column the oil discharged from said upper bank of tubes, dampers for said ports and means responsive to the fluctuations produced in the temperature of the oil flowing through said upper convection tubes for controlling the setting of said dampers to vary the amount of hot products of combustion passing through the ports and thus by-pass said upper bank of tubes.

9. A system for distilling petroleum oil comprising a heater of the bridge wall type, a first fractionating column, a second fractionating column, a combustion chamber in said heater, a convection chamber in said heater, a bridge wall having ports therein disposed between said combustion and said convection chambers, means for introducing hot products of combustion into said combustion chamber, means for conveying said hot products of combustion over said bridge wall and thence downwardly through said convection chamber, oil-confining tubes in said combustion chamber, an upper bank of tubes in said convection chamber and disposed above the level of said ports, a lower bank of tubes in said convection chamber and disposed below the level of said ports, means for causing oil to flow through said lower bank of tubes, thence to said first iractionating column wherein the vaporized oil is fractionated from the unvaporized condensate,

means for conveying said condensate as a separate stream through the tubes in said combustion'chamber for heating therein, means for conveying the heated oil from said combustion chamber to the upper bank of tubes in said convection chamber for further heating therein, means for conveying to said second fractionating column the oil discharged from said upper bank oi. tubes, dampers for said ports and means responsive to the temperature 0! the oil at the discharge end of said upper bank of tubes for controlling the setting of said dampers to vary the amount of hot products of combustion passing through the ports and thus by-pass said upper bank of tubes.

10. In a heater for heating at least two separate streams of fluid, a combustion chamber, a convection chamber, a bridge wall having ports therein interposed between said chambers, means for introducing hot products of combustion into said combustion chamber, means for causing the hot products of combustion to flow upwardly in said combustion chamber, thence over said bridge wall and through the ports therein and thence downwardly through said convection chamber, fluid-confining tubes in said combustion chamber and adapted to be heated by said hot products of combustion, a bank of fluid-confining tubes in said convection chamber and located above the level of said ports, another bank of fluid-confining tubes in said convection chamber and located below the level or said ports, a connection for conducting fluid in series from said tubes in the combustion chamber to one of the said banks of tubes in the convection chamber, controlled dampers for varying the area of said ports to vary the amount of hot products of combustion passed therethrough, and means responsive to the fluctuations produced in the temperature of the fluid flowing through said upper tubes for controlling the means for introducing hot products of combustion into said combustion chamber.

. GEORGE W. WA'I'IS. 

